Transport Secretary John Prescott has promised a public inquiry into the crash and praised the "swift efforts of all the emergency services".

Conservative Transport spokesman John Redwood said: "We need a proper inquiry and we need some answers for the future."

The trains collided on the same stretch of line as the Southall rail crash in 1997, in which seven people died and 150 were injured.

Health and Safety Executive inspectors are at the scene.

In Context
Investigations revealed how 31 people died and dozens were injured because of a head-on collision when one of the trains passed a red signal.

Public inquiries were headed by Scottish judge Lord Cullen. He made dozens of safety recommendations and concluded Railtrack, the company then in charge of rail infrastructure and its investment, had failed to respond to earlier warnings about signalling problems.

He also criticised the Health and Safety Executive's Rail Inspectorate and recommended an independent Rail Industry Safety Body.

Thames Trains was fined a record £2m in April 2004 for breaking health and safety laws. The court was told the train driver had not been warned about problems with the signal at Ladbroke Grove and had not received adequate training.

In December 2004 the Paddington Survivors' Group complained that many of the safety recommendations made after the crash in 1999 had still not been implemented.

A year later, in December 2005, the Crown Prosecution Service said no individuals would face criminal charges over the crash as there was
"insufficient evidence" to provide a realistic prospect of conviction".

In October 2006, Network Rail admitted health and safety breaches concerning the siting of the signal. It is likely to receive a heavy fine when sentence is handed out in December.